Tuning device for radio receivers



April 15,1941- F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS FiledSept. 1, 1938 4 Sheets-Sheet 1 SPEAKER TERMINALS ll l-L INVENTOR FRANKALLENZ/TCHELL BY ATTORNEY April 15, 1941. F. A. MITCHELL 2,238,475

TUNING DEVICE FOR RADIO RECEIVERS Filed Sept. 1, 1958 4 Sheets-Sheet 2:Qm o

OFF 1Q 0 i5 o l al 2 w.

INVENTOR FRANK LE MITCHELL #i wwl L/ Afro/um April 15, 1941.

F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS Filed Sept. 1, 1938 4Sheets-Sheet 3 F1 19. INVENTOR FRAN/(Al NM/TC/IELL 7% from/5r April1941- F. A. MITCHELL TUNING DEVICE FOR RADIO RECEIVERS 4 Sheets-Sheet 4Filed Sept. 1, 1938 ITCHELL INVENTOR FRANK AL EN By W A TTORNEY PatentedApr. 15, 1941 7 2,238,475 TUNING DEVICE roa aanro aacnrvnas Frank AllenMitchell, London, England, assignor to Electrical 8; Musical IndustriesLimited, Mlddlesex, England, a com any of Great Britaln ApplicationSeptember 1, 1938, Serial No. 227,881 In Great Britain September 1, 1937Claims.

This invention relates to tuning devices for radio receivers of the kindin which the tuning device can be rotated to one or other of apluralit'y of predetermined positions by the oper ator either at thereceiving apparatus or from a remote point. I

Proposals have heretofore been made whereby a radio receiving apparatusmay be tuned mechanically under the control of the operator as, forexample, by depressing one'of a plurality of push buttons which causesrotation of a tuning condenser by energising an electric motor, thetuning condenser being rotated by a predetermined amount after which itis brought to rest in the desired station receiving position.

Other proposals have also been made but most of these are notsatisfactory owing to the complication of the mechanism employedresulting in large manufacturing costs, service difliculties anduncertainty in operation.

It is the chief object of the present invention to provide an improvedtuning control-for automatically rotating a tuning device, for example,a tuning condenser, into a plurality of stationreceiving positions underthe control of the operator either at the receiver or from a remotepoint.

Accordin to the invention the tuning control comprises a selector memberhaving conducting and insulating zones thereon and a plurality ofelectrical contact members in engagement with said selector member so asto be capable of contacting with the insulating or conducting zonesthereon, some of said contact members serving to control directly or tooperate relays to control an electric motor for rotating said selectormember and a tuning device connected thereto to predetermined positions,the arrangement being such that when a selected contact member is inengagement with an insulating zone of the selector member the electricmotor is rotated in one direction and when a selected contact member isin engagement with a conducting zone the electric motor is caused torotate in the reverse direction.

In the preferred form of the invention the selector member comprises adisc directly coupled to the shaft of the tuning device which, in mostcases will be a variable condenser, the disc generally being ofconducting material but having an insulating zone thereon, saidinsulating zone being so formed that during rotation of said disc thecontact members bear either on the conducting or the insulating zones ofsaid disc. The disc is arranged to be angularly moved through with thetuning condenser and the Junction between the insulating and theconducting zones of said disc is preferably of serrated iorm and duringangular movement of said disc an edge of each serration moves past acorresponding one of said contact members. The tuning control may beoperated by a selector mechanism of the type disclosed in United StatesJating zones associated with the particular contact member. If, ondepressing one 01' said push buttons, the associated contact member isin engagement with the insulating zone of said disc,

then the tuning condenser would be rotated in one direction, but if theselected contact member is in engagement with the conducting zone ofsaid disc, then the tuning condenser will be rotated in the oppositedirection.

In order that the present invention may be clearly understood andreadily carried into eflect it will now be described with reference tothe accompanying drawings in which:

Figure l is a circuit diagram of a tuning ccntrol in accordance with theinvention,

Figure 2 is an enlarged view of the selector member,

Figure 3 is a plan view of a selector box having a plurality of pushbuttons for use in the invention.

Figure 4 is a plan view of the underside of the box shown in Figure 3with the bottom of the box removed,

Figure 5 is a cross-section view taken along the line 8-5 of Figure 4with the bottom of the box in position,

Figure 6 and Figure 7 are respectively side elevation and plan views ofa modification showing another selector member which may be employed inaccordance with the invention,

Figures. 8 and 9 show different methods of supporting and adjusting thecontacts on ihe selector member,

Figure 10 illustrates an alternative form of selector box having aslidable selector, and

Figure 11 is a circuit diagram of another modiflcation having asimplified form of selector member using circumferential adjustment forthe contact members which may be employed in accordance with theinvention.

Referring now to Figure l of the drawings, the mechanism in accordancewith the invention comprises a selector member 5 which, as shown indetail in Figure 2, comprises a disc of metal I, the metal constitutingthe aforesaid conducting zone whilst the zone of insulating material 8is recessed into the surface of the disc or arranged in an aperturestamped out from the disc. As aforesaid, the disc is rotated with thetuning condenser, not shown, and arranged for rotation through an angleof 180 by a reversible electric motor hereinafter referred to. Arrangeddiametrically of the disc 1 is a plurality of contact members A-O, asshown in Figure 1, the contact members being mounted ina block 9 ofinsulating material the ends of the contact members having contactelements which bear on the surface of the selector disc I. Since thedisc rotates only through 180", eight of the contact members arearranged on the righthand side of the disc and the other seven contactmembers are arranged on the left-hand side, as shown in Figure 1, thedisc '5 having insulatin zones arranged in the manner hereinafterreferred to. The contacts A, B, C, D, E, F, G, and the contacts H, I, J,K, L, M, N on either side of the disc serve as station selectorcontacts, the function of the remaining contact 0 being hereinafterreferred to. The junction between the conductor and insulating zones ofthe disc is, as shown in Figure 2, of serrated form providing edges ill.An edge is is provided for each contact and each edge is spaced radiallyfrom the centre of the disc a distance such that it is adapted to movein a path which will bring it into engagement with its associatedcontact 4 member. Referring to Figure 2, the selector member is shown inits extreme position of movement in ananti-clockwise direction and theedges H! at the upper half of the member 6 are adapted to move intoengagement with their respective contact members A G when the selectormember is moved in a clockwise direction. Similarly the edges to at thelower half of the member 6 are adapted to move into engagement withcontacts H N when the selector member is rotated in a clockwisedirection.

The edges ID of the insulating zone are spaced angularly round theselector member so that the The arrangement of the apparatus is suchthat the selector member and tuning element of the radio receiver arebrought to rest when an edge Ill of the insulating zone of the selectormember lies substantially in engagement with the selected contactmember, and the radio receiver is "tuned in to receive a selectedstation when the tuning element is in that position, as will bedescribed more fully hereinafter. Each of the contact members A-O isconnected by the leads shown to a corresponding number of socketsmounted on a plug panel indicated by the dotted line it, the plugsockets being lettered with the same lettering as the contact members.To select a particular station, in the example shown in Figures 1 to 5,one of a plurality of five push buttons i2 is depressed, the pushbuttons being associated with selector and switch controls mounted in aselector box shown in detail in Figures 3, a and 5. For the sake ofconvenience in Figure 1 only one push button it? and associated selectorswitch contacts are shown and five sockets A, D, H, I and M areconnected by a single lead to one of the switch contacts although itwill be understood that each or" the said sockets will, in practice, beconnected by a separate lead to the appropriate switch contact or" therespective one of the iive push buttons shown in Figure 3. If desired,the selector box 52 may contain fourteen push buttons for associationwith the fourteen contact members A@ and H-N, but in the arrangementillustrated in Figures 8, e and 5 where only five push buttons areemployed, a removable multipin plug may be provided whereby the pushouttons may be connected to any group of five contact members accordingto the requirements of the operator. The selector box or panel may bemounted on the cabinet of the radio receiver or in a position remotetherefrom and connected to the plug panel by a flexible or other leadtermh mating in the removable plug, or, if desired, several selectorboxes or panels may be connected to the same radio receiver.

Each selector switch comprises a push button l2 projecting through anaperture in the selector box and a bank of switch contact fingers it,it, i5, i6 is located beneath the push button. The uppermost contactfinger it is insulated fiomthe push button bye strip ll of insulatingmaterial and is adapted to engage with contact finger l5 to close acircuit when push button I? is de pressed. Coniact finger i5 isinsulated from contact it by the strip it of insulating material and,when depressed by movement of the push but ton, contact finger l5 causescontact finger it to engage contact finger it to close a second circuit.The lowermost contact l3 lies adjacent the metal base plate of theselector box, which plate is connected to earth in any suitable manner.A plate of insulating material it is mounted on the metal base plate sothat the contact ilnger i3 is insulated from the base plate along aportion of its length, but the arrangement is such that the endofcontact finger it under the push button i2 is adapted to come intocontact with the base plate when the push button is depressed to close athird circuit. When a push button is depressed all of the contactfingers i3, i4, i5 and I6 are depressed and when the push button isreleased it is held in an intermediate position by a latch 20, which iscommon to all of the push buttons, as shown in Figures 4 and 5, thelatch being operated by a relay 2i and released as hereinafter referredto. The latch 28 comprises a bar pivoted on trunnions 2?; and the end ofeach push button is provided with a shoulder 23 with which the latchengages when the relay is energised to draw the latch towards the push.button.

Direct current for the operation of the relay 2i, and further relayshereinafter described, is derived from a contact rectifier 24 connectedto a secondary winding 25 of a. mains transformer indicated generally at25. The selector member 6 and the tuning condenser are rotated by areversible electric motor which, as shown, may be an induction discmotor and is supplied with current by tapping the primary winding 2! ofthe transformer, as shown. The electric motor has a main current winding28 and two voltage windings 29 and Elli which control the direction ofrotation of the motor, only one of said voltage windings being incircuit at a time. Current is supplied to the motor on depressing one orother of the push buttons l2 through the medium of a relay 3|. The relay3| is associated with contact iingers 33, I4, 35, 33, 31, 38, and 33,which are normally maintained apart, as shown in Figure 1, but which,when the relay 3| is energised, as hereinafter described, are closed,the contact finger 33 engaging contact finger 34, contact fingers 35, 36and 31 engaging one another, and contacts 38 and 33 likewise engagingone another. A further relay 32, is provided, associated with contactfingers 40, 4|, 42, 43, 44, 45 46, 41 and 48, which are normallymaintained in the positions shown in Figure 1, but which, when the relayis energised, as hereinafter referred to, are closed in the followingmanner. The contact 4|! is moved out of engagement with contact 4| andthe contact 42 moved into engagement with 4|. Contact 43 is moved out ofengagement with contact 44 and contact 45 moved into engagement withcontact 44. Contacts 48 and 46 are engaged and thereafter contact 43moved out of engagement with contact 41. Relay 3| controls the supply ofcurrent to the current coil 28 of the motor and also to the changeoverswitch represented by contact fingers 40, 4|, 42 which permits currentto how through one or other of the potential coils 29, 30 of the motor.

Relay 32 controls the direction of rotation of ie motor and whenenergised opens the circuit of potential coil 3|! which energises themotor to rotate the selector disc in a clockwise direction and closesthe circuit of potential coil 29 to reverse the direction of rotation ofthe motor and cause movement of the selector disc in an anti-clockwisedirection. The various switch contacts associated with the relays 3| and32 are connected to the motor, to the contacts associated with theselector member and to the contacts of the selector box, as shown, thecontacts 31 and 45 being connected to' earth. The mains transformer 23may be the same transformer that supplies current for the operation ofthe radio receiving apparatus and, as shown, further secondary windingsare provided for heating the valves and Supplying operating potentials,the secondary winding 49 supplying current to the cathodes of the valvesthrough normally closed contacts and a further secondary winding 5|supplying current for the rectifier valve of the receiving apparatusthrough normally closed contacts 52, whilst' a pilot lamp 53 normallyderives current fromthe primary 21 of the transformer through normallyclosed contacts 54. The function of the contacts 5!, 52 and 54 will behereinafter referred to.

The operation of the mechanism is as follows. Assuming that it isdesired to select a station represented by the contact M, and that theselector disc is, as shown in Figure l, in its extreme position ofanti-clockwise rotation so that contact M bears against the insulatingzone of the disc, then the appropriate push button i2 is depressedwhich, closes the contacts l3 and i4 and causes contact i3 to bearagainst the earthed plate of the selector box. Earthing of contact i3closes a circuit which includes the transformer secondary 25, rectifier24, relay 3|, conducting lead R, switch contact I3, earth plate of theselector box and so to earth and back to the transformer winding 25.Relay 3| is thus energised and closes switch contacts 3334. Closure ofswitch contacts 3334 completes the driving motor circuit and currentflows from transformer primary 21, switch contacts 33, 34,

ear'thed plate.

current coil of motor, and back to the transformer primary 21.- Currentalso flows from switch contacts 33, 34 to the closed switch contacts 40,4| controlled by relay 32, potential coil 30, and back to transformerprimary. The driving motor is thus energised, and since potential coil30 is energised the selector disc and the tuning element of the radioreceiver will commence to rotate in clockwise direction, and the edge inof the insulating zone of the selector disc will move towards contact M.

Referring again to the selector switch, pressue upon push button |2 hasalso brought switch contact |4 into engagement with contact member I3. Afurther circuit is thus closed which includes transformer secondary 25,rectifier 24, lead U, relay 2| in the selector box, contact members I4and I3, earthed plate of the selector box and transformer secondary 25.Relay 2| is then energised, and the latch 20 is drawn into position tolatch push button |2.

It will be understood that the energisation of relays 3| and 2|, theclosure of the various contacts controlled by relay 3| and movement oflatch 20 of relay 2| is effected instantaneously, and after a momentarypressure has been applied to press button l2, pressure upon the pressbutton may be removed so that the bias of the switch contact blades willreturn it to an intermediate position in which it is latched by thelatch 20. When the push button i2 returns to its intermediate positionselector switch'contacts |3, |4 remain in engagement, but contact isbroken between switch contact I3 and the The motor controlling relay 3|and the selector box latching relay 2| continue to be energised,however, through the following circuits: terminal R of relay 3|,resistance l3, closed switch contacts 46, 41 of relay 32, switchcontacts 35, 36 and earthed contact 31 of relay 3|, which are closedsince relay 3| is energised. Current also flows from contact S on relay2| through selector switch contacts l4, l3 and resistance l3.

Referring again to the act of pressing the selector switch push buttonl2, this action also causes contacts |5, IE to close, and the saidcontacts are connected in a circuit which includes thefearthed selectordisc, contact member M,- socket member M on plug panel selector boxswitch contacts l5, i6, lead Q, switch contacts 46, 48 of relay 32 whichare at present open, since relay 32 is not energised.

As stated hereinbefore, the selector disc is rotating in a clockwisedirection and the edge ill of the insulating zone is moving towardscontact element M. As soon as rotation of the selector disc issufficient to cause the contact element M to pass from engagement withthe insulating zone to engagement with the conducting zone of the disc,relay 32 is energised through transformer secondary 25, rectifier 24,relay 32, lead Q, closed contacts 38 and 39, selector switch contacts|6, |5, socket M on plug panel H, contact member M, selector disc, earthand so back to transformer secondary 25.

Energisation of relay 32 causes changeover switch contacts 40, 4|, 42 tobe reversed thus deenergising voltage coil 30 of the electric motor andenergislng voltage coil 29 of the motor. The direction of rotation ofthe motor and thus of the selector disc 6 and the tuning element isreversed and the selector disc is rotated in an anticlockwise directionto bring the insulating zone of the selector disc intoengagement withthe contact element M.

Energisation of relay 32 also causes contact member 48 to engage withcontact member 48 to provide alternative path for current flowingthrough relays 3|, 2| and resistance l3 and immediately after contacts48 and 48 engage contact 46 is disengaged from contact 41. The effect ofthis is to transfer control of relays 3| and 2| from switch contacts 35,38, 31 of relay 3| to the selector disc and current now flows fromrelays 3| and 2|, through resistance 13*, switch contacts 46 and 48 ofrelay 32, lead Q, switch contacts l8, ii, of selector switch, contactsocket M of plug panel ll, contact member M, the conducting zone of theselector disc and so to earth.

The motor continues'to rotate the selector mernber in an anti-clockwisedirection, after relay 32 has been energised, until the contact M bearsagainst the insulating zone of the selector member and when thisposition is reached the circuit for the motor is disconnected throughthe opening of the contacts 33 and 34 on relay 3!; The deenergisation ofrelay 2| which occurs at the same time as de-energisation of relay 3|owing to the circuit being broken by contact member M bear-. ing againstan insulating zone, causes the push button of the selector switch to beunlatched and thus allows switch contacts l3, I4, I! and I8 to beopened, and the press button l2 to be returned to its off position dueto the return movement of uppermost contact finger l8. Relay 32 is thusde-energised since the contacts l5, l8 have opened. In this position the.tuning cbndenser has/been rotated to a position to tune in a-stationrepresented by contact M, the selector meniber 8 having been rotateduntil, as above mentioned, the contact M is in engagement with theinsulating zone of the selector disc. ,"I'hreceiving apparatus is thustuned to the/required station and the relays and the motor arede.-energised and the various contacts ,are returned to" the positionsshown in the drawing;

When the desired station has been tuned in and the relays have thus beende-energised, it will be possible to operate the tuning mechanism fromanother selector box 82 located in another position but connected to theplug panel II by parallel circuits.

In some cases the position of the selector disc I may be such that theselected contact member is bearing upon a conducting zone of theselector disc. In such cases relays 2|, 3|, and 32 will all be energisedsubstantially simultaneously when the press button is depressed and thevarious contacts operated by the press button, and relays 3| and 32 willbe opened or closed in the manner hereinafter described, ,so that themotor rotates the selector disc in an anti-clockwise direction .untilthe selected contact member engages with the insulating zone of the discto de-energise relay 2I and 3| and to cause the circuit of relay 32 tobe de-energised.

It will be appreciated from the above that when the stationary contactof a selected station bears against an insulating zone of the selectormember, relay 3| will be energised 'so that the motor rotates theselector member 8 in a clockwise direction. Conversely, when the contactmember of a selected station bears against a conducting zone of theselector member 6, the selector member will be rotated in ananti-clockwise direction.

It will also be appreciated from the above that although the selectordisc may move in either dijustments of the apparatus to be made withgreat accuracy.

A radio receiver to which the invention may be applied will, in mostcases, be provided with the, usual manual control and it, for example,during such manual control, the selector member 6 is rotated in aclockwise direction from the position shown in Figure 1 through it willbe seen that the right-hand contacts on the selector member aretraversed first by the insulating-zone and then by the conducting zoneand one or more contact members mayengage the insulating zone again inthis extreme position. If one of the contact members bearing against theedge of the insulating zone were selected, the result would be that onlythe relay 3! would be energised and the selector member would be rotatedin a clockwise direction, whereas. the apparatus requires that underthese conditions the selector member should rotate in an anti-clockwisedirection. To obtain this reversal of rotations to an anti-clockwisedirection in the extreme position, it is necessary to arrange for therelay 32 to be energised when a push button is depressed. This iseii'ected by so'shaping the conducting zone of the selector member 8 asindicated at 58 so that when the selector member is in the positionabove-mentioned the contact G bears against the conduct.- ing zone 88.The contact G, as will be observed from Figure l, is connected to thecontact 38 of relay 3| and when the relay 3| is energised the contact 39is moved into engagement with contact 38 with the result that currentthen flows through relay 32, the contacts associated with the relay 32are operated as above described and, the direction of rotation of themotor is reversed To enable the receiving apparatus to be switched outof operation-from the selector box, a further button HA is provided asshown in Figure 3, this button being connected to the contact Own theselector member 8 so that when the button HA is depressed the selectormember 8 is rotated in an anti-clockwise direction until the extremeposition is reached. It will be observed i'rom Figure i that the contact0 is normally in engagement with the conducting zone I, but in theextreme position it comes into engagement with the insulating zone,which is specially shaped for this purpose, as indicated at 51. Theselector member is therefore brought to rest in this position. Thecontacts 58, 52 and 54 are mounted adjacent the selector member 8 and astriker 58 is provided on the selector member so that in the extremeposition of said member the striker engages the contacts to open thecircuits controlled thereby so that the current to the receivingapparatus is switched off;

' The contacts 38 and 31 associated with relay 3| and contacts 44 and 45associated with relay One such arrangement suitabl ior a moving.

coil loudspeaker with a permanent magnet is illustrated in Figures 1 and4 of the drawings.

output transformer of the radio receiver, the primary winding of whichis not shown, is earthed at one end and'the other end is connected toswitch contact 44 of relay 32. A lead from contact 43 is connected toone oi two plug sockets 59 and the other plug socket is connected to theadjustable arm 40 of a potentiometer the resistance element 05 oi whichis connected at one end as illustrated in Figure 1 to the lead fromcontact 43 and at the other end to contact O or plug panel II and so toearth.

The plug sockets I! are adapted to receive the speech coil leads of aloudspeaker, not shown, and the strength of the repmduced sounds may becontrolled by adjustment of the arm of the potentiometer which isprovided with a suitable control member projecting through the selectorbox and terminating in a control knob 0|.

It'will be appreciated that the distance between adjacent edges II ofthe selector member 0 corresponds to a range oi adjustment of the thevertical heights of the station selector contacts bearing against theselector member I, it is possible for the operator to select what staticns he may require to be selected on operation oi the push buttons. Toenable the operator to adjust the station selector contacts, it isprei'erred to mount the station selector contacts in such manner in theinsulating block 0 that their vertical positions can be adjusted. Forthis purpose the station selector contacts may be held in grooves orslots in the block I and screws may be provided in engagement with thecontacts so that on rotating the screws the vertical positions of thestation selector contacts can be adjusted.

It will be understood that if desired a number of selector discs andassociated contact members may be employed and, furthermore, instead ofemploying selector discs, drums or cylinders may be used.

Reference is now made to Figures 6 to 9 of'the accompanying drawingswhich show a modified form of selector member and contacts that may beemployed in accordance with the invention.

In Figures 6 and 7 the tuning device of the receiver is shown as acondenser IOI and the cabinet front of the receiver is shown by thechain line I02.

The station locating mechanism is preferably supported entirely on thecondenser mounting plate I III to keep strict relation between the partsand to minimise vibration.

The station selector member in the form 01' a disc I03 is rigidlymounted on the condenser shaft I which also carries the usual stationindicating pointer I00. The selecting member I03 is engaged by thefriction drive I01 which is adapted to be rotated in known manner bymeans of the hand operated knobs I, or by an electric motor (not shown)such as the motor described in connection with Figures 1 to 4 of theaccompanying drawings which is coupled to the control shaft 9.

. 10 The secondary winding 44 (Figure 1) of the The mounting plate I I 0also carries a plurality of contact members III to III in springengagement with the selector member 3, the contacts III to H9 beingmounted in grooves cut in a block I20 of insulating material rigidlyattached to the plate II. The plate III also rigidlygsupports the frameI2l, which carries adjusting means whereby the contacts III to III maybe adjusted to predetermined positions.

The contact members III to II! are each preferably in the form of a fiatstrip of spring-y metal having a contact point I22 at one end and bentto a.V shape at the opposite end, as shown in Figures 8 and 9, so thatpressure on the short limb will keep the contact strip III located inits groove in the block I20. The extreme end of the short limb is bentat right angles and engages the recessed end I23 of an adjusting leverI24 pivoted at I25. The lever I24 has a toothed segment I20 formedthereon which is engaged by a screwedadjusting member I2'I mounted onthe frame I2I carried-by the mounting plate IIO as tuning condenser and,consequently, by adjusting hereinbefore mentioned. Each lever I24 isspaced from adjacent levers by a spring pressed nonrotatable spacer I32whereby they are adjustable independently. The screw I2! is mounted sothat it has no end play, but can be rotated by the knurled head I28 orby the slotted head I29 to rotate the lever I24 and thereby move thecontact strip III and contact I22 angularly relative to the stationselector disc I03. Similar adjustment means may be provided for thecontact strips III to III.

Each of station selecting contacts, III to II! is adapted to operate inconjunction with one of the stepped edges of an insulated zone I04 asdescribed in connection with Figures 1 to 5.

The zone of insulation I04 formed on the selector disc I03 is formedwitha plurality of radially spaced steps, as shown in Figure 7, soarranged that the adjustable contacts III to H0 may be supported inparallel relation and with their contact points lying approximatelyalong a line radial to the disc I03. The adjusting levers I24 may thusbe mounted on a common shaft I25 supported by the frame HI and thescrewed adjusting members I21 may be arranged in one or more linesparallel to the shaft I25. The ends of the adjusting members I21preferably pass through apertures in a panel I33 mounted on the frameI2I and the panel is 1 located in an aperture in a wall of the cabinetwhereby adjustments may be made from the exterior of the cabinet. Thepanel may be provided with waveband or other markings to indicate thefrequency range of each adjustable contact of the rotary switch.

Figure 8 shows a modified form of adjustment device I24 for theadjustable contacts III to III.

The lever I24 is formed with a projection I 2411 which is located in arecess in the contact III, and the edge I26 oi the lever is providedwith teeth which mesh with a worm I2I. The worm shaft carries a knurleddisc I 28 which projects through an aperture in a wall of the cabinetand is adapted to be rotated to adjust the contact III.

Figure 9 shows a further modification of the adjustment device I24wherein the lever itself projects through an aperture in the cabinet andmay be rotated to adjust the contact III.

Referring now to the modifications shown in Figures 10 and 11 of theaccompanying drawings the station selector mechanism shown in Figure bya chosen station name is selected, and a single press-button 223 adaptedto put the contact member 20i into operative circuit with the relays sothat they function in the some manner as described with reference toFigure 1. In selector panel unit Figure 10, 222 may be connected to theplug panel ii in place of or in parallel with the press button box 52 inFigure l, and the remainder of the circuit beyond the panel i i mayremain as in Figure 1.

When a desired station is to be selected, the sliding contact 205 ismoved to the desired stud 204 (c for example) to connect the adjustableContact member operating on the disc 6 (Figure 1) to the spring contactfinger 205 (Figure 10). The actuating button 203 is then pressed toclose contact fingers 205, iii and i4 and contact fingers i5 and i5.This permits current to flow from the rectifier 24 (Figure 1) throughmagnet 206, contact fingers i4, 205 to earth through connector P asdescribed with reference to Figure 1, to cause magnet 206 to hold thecontacts to and N as well as I3 and it closed so that current is thenable to flow from the rectifier 24 through relay 3i (Figure 1) and theholding magnet 20B re turning to earth through connection R. andresistance I 3A as described with reference to Figure l. Thepress-button is returned as soon as the operators finger is removed, bythe spring contact 205, the magnet 200 keeping the circuit active untilthe desired station is found. In the modification illustrated in Figurethe electrical components of the complete mechanism operates exactly asdescribed with reference to the circuit of Figure l. The magnet 208becomes demagnetised when the desired station is found and the selectorpanel contact fingers i3, l4, l8 and I5 return to their neutral positionto break the circuit through the slider 2% so that any other station maybe selected on it or on another panel or press-button selector workingin parallel therewith.

The above selector mechanism shown in Figure 10 or the press-buttonpanel (Figures It, 55, 4 and 5) can be built into a portableloud-speaker case, the connections 59 (Figure 1) being permanentlyconnected to the loud-speaker. The case or the panel may sometimes carryan additional switch or press-buttons to operate a wave-change device.such as a relay, on the wireless receiver, for on ample in the mannerreferred to in U. 8. Patent No. 2,100,609 previously referred to.

Another modification of the invention is shown diagrammatically inFigure 11 in which the disc 2% of insulating material has a metalsegment 208 inserted therein so that the surface of 2b? and 208 arefiush. The disc is rigidly attached at 209 to the rotatable tuningelement of a wireless receiver and the whole is adapted to be driven bythe reversible electric motor 2 iii. A plate preferably of insulatingmaterial 2 is non-rotatably mounted in front of the rotatable disc 20?and carries a number of sliolable contact members 2l2 capable ofadjustment into desired station selecting positions in the followingmanner. The tuning element (not shown) is first turned by hand until thedesired station is in tune, then one of the contact members 2l2 isreleased by means of the-screw H3 and is slid around the slot 214 untilthe contact edge 2!? lies on the insulated portion close to the edge 26Eof the metal segment 2055. The screw 253 is then tightened and the nameor cypher for the station inserted in the control box or panel 2Wagainst th press-buttom switch or stud by which the r or is reversedwhereupon contact 22'! opens.

the use of relays the circuit may be arranged as I shown in Figure 11,in which the control panel 217 has a series of press-button 230, eachopen ating a. contact finger 2l8 connected by a separate lead 288 to itsassociated contact member 2l2. The A. C, supply indicated conventionallyin Figure 11, from the mains or a. transformer (at 25 volts for example)is connected to the contact finger 220 which is preferably in the formof a comb so as to be common to all the independent contact fingers 2l8.The other side of the A. C. supply is connected to the current coil 22]and the potential coil 222 of the (induction) motor 2I0. The oppositeside of the current coil 22! is connected to the metal segment 208 onthe disc 201.

The contact fingers 223 are connected to the opposite side of thepotential coil 222, and the above connections are suflicient to causethe motor to run in one direction for example, clockwise, if theselected contact 2l2 happens to be on the metal segment 208. To enablethe motor to run in the opposite direction when the circuit is notcomplete through 208 and 2l2 a suitable condenser 224 is insertedbetween the current coil 22i and the A. C. supply so as to change thephase between the coils 22l and 222. This is achieved by using anothergroup of contact fingers 225 adapted to permit current to flow throughthe condenser 224 when the press button 230 is fully depressed by hand,so that 225 touches the contacts 220A which are connected to the A. C.supply and which will cause the motor 2) to rotate the disc 201 in areverse (1. e. anticlockwise) direction while the condenser 224 is notbeing shorted by contacts 208 and 2l2.

If the circuit were left as above, the motor would tend to hunt when thecontact edge 215 reached the edge 2? of the metal plate, and to preventthis it is desirable to attach a friction disc device 226 on the motorshaft so as to close a contact 221 when rotating in one direction forexample in an anti-clockwise direction. The contact 227 closes a D. C,circuit which may be from a battery H. T, radio or a separate rectifierto operate the magnet 228 to hold the contacts 225 and 220A togetheruntil the motor 2I0 stops The contacts H8, 220 and 223 are held closedby the mechanical latch 229 in known manner, and will release theselector contact finger 2l8 when another button is pressed to selectanother station or to disconnect the control.

The above circuit arrangement functions similarly to that described withreference to Figure 1, as follows. When a station is to be selected andthe chosen contact 212 happens to be in the insulated portion of thedisc 201, the action of pressing the button 230 closes all the contactfingers 2l8, 220, 223, 220 and 220A, but as there is an open circuitbetween 208 and 2l2 current only flows between 220, 223 and coil 222 andbetween 220A, 225, condenser 224 and coil 22! whereby the motor rotatesin an anti-clockwise direction and closes contact 221 to energise magnet228 to keep 220A and 225 closed so that the motor continues to rotatethe station selector disc 20'! and tuning element in an anti-clockwisdirection until the contact edge 2|! touches the plate edge 216. Whenthis occurs A. C. current immediately flows through the lead 2|! directto the current coil 22!, thus reversing the motor and opening contact22! whereby contact fingers 220A and 225 are opened: at the same timethe disc 20'! is slightly reversed so that the edge H5 is again on theinsulated portion 201 and no A. C. current can then reach the coil 22|through lead 219 or condenser 224 and therefore the motor stops, leavingthe disc 20! and the tuning element in the desired tuned position.

Similar arrangements as have been described in connection with Figure 1to provide rotation of the electric motor in an anti-clockwise directionwhen the selector member has been rotated to its extreme clockwiseposition and for breaking of the circuit by means of the insulating zonebeing shaped as at 56 and 51, Figure 2 may be provided in themodification described in connection with Figure 11 of the accompanyingdrawings by suitable shaping the insulating and conducting zones of theselector member 201.

The above circuit arrangements should mechanically tune a wirelessreceiver with sufllcient accuracy for all frequencies below 1500 kc.(above 200 meters), but if higher frequencies are required or if easieradjustment is desired, it is advisable to make use of automaticfrequency control" in the radio circuit in addition to the above. I

I claim:

1. In a tuning control for radio receiving apparatus provided with anadjustable tuning element, a selector member having a surface providedwith conducting and insulating zones, a plurality of electrical contactmembers in sliding contact with the surface oi the selector member, areversible motor for driving both said tuning element and the selectormember, a motor circuit for connecting the motor to a source ofenergizing current including said contact members and a plurality ofoperable relay devices for controlling the operation of said electricmotor so as to adjust said selector member and said tuning element topredetermined positions, said motor circuit being arranged so that whenthe motor is energized through a selected one of the contact memberswhich is in engagement with an insulating zone of said selector member,the electric motor is rotated in one direction and when a selected oneof said contact member i in engagement with a conducting zone of theselector member the electric motor is caused to rotate in the reversedirection.

2..In a tuning control arrangement for radio receiving apparatus asdescribed in claim 1, a pair of voltage windings for said reversibleelectric motor, said voltage windings being arranged to control thedirection of rotation of the motor, only one of said voltage windingsbeing connected in the circuit during any one operation of the motor.

3. In a tuning control arrangement for radio receiving apparatus of thetype described in claim 1, a pair of voltage windings for said electricmotor to control the direction of rotation thereof, a source of energyfor said motor, a condenser and means for applying energizing energyfrom. said source to the motor through said condenser when the selectedcontact is in contact relation with an insulating zone of the selectormember so as to cause the motor to rotate in a reverse direction towhich it is caused to rotate when the selected contact is in contactwlth'a conducting zone of the selector member.

4. In a tuning control arrangement for radio receiving apparatus asdescribed in claim 1, a plurality of selectively operable meanscorresponding to said electrical contact members and adapted to selectupon operation any one of said contact members comprising push buttonsany one of which is adapted to be depressed to select the correspondingcontact member, latching means for holding the depressed one of saidpush buttons in a depressed position during operation of the motortuning means and means for automatically releasing said push button uponcompletion of the tuning operation.

5. In a tuning control arrangement as described in claim 1, change-overswitching means connected in said motor circuit and efl'ective only whena desired predetermined position of the tuning element is approachedfrom one direction, for causing the motor to move the tuning elementbeyond the desired position and reversing the direction of rotation ofthe motor so as to move the tuning element back toward the desiredposition whereby the final rotation in adjusting the tuning element to arequired position is always made in the same predetermined directionirrespective oi the initial direction of rotation of the tuning element.

FRANK ALLEN MITCHELL.

